Especially in the aerospace industry, there is a requirement for fasteners with certain characteristics that make them suitable for securing removable panels. This type of panel is attached to a supporting structure by a number of fasteners that frequently must have the capability of resisting shear loads. This is accomplished by a bolt shank that extends through an opening in the structure to mesh with a nut held to the opposite side. Because of the loading, the shank of the bolt portion of the fastener has been made relatively large in diameter so as to have a cross sectional area sufficient to enable the fastener to withstand the shear forces.
However, when the large threaded shank is pushed or pulled through a generally complementary opening in the supporting structure as the panel is installed or removed, there is a tendency for the shank to ream out the opening, especially when the support is made of relatively soft material such as aluminum. Obviously, this is undesirable and causes permanent damage. In addition, the large shank may catch on the wall of the opening when the panel is to be removed, making it difficult to separate the panel from the supporting structure. With the shank of the bolt being approximately as large in diameter as the opening through which it extends when the panel is secured, precise alignment with the opening is necessary for attachment of the panel. This adds to the time and the difficulty in securing the panel in place.
One form of extensively used panel fastener includes retainer ring that slides along the bolt shank and serves to retain the bolt to the panel. This retainer ring is exposed when the fastener is separated, leaving it vulnerable to damage or to being dislodged from the shank. This fastener also requires the formation of close tolerance grooves in the shank which must be produced by expensive EDM machining. This adds substantially to the cost of the completed fastener.